The immune system usually has no trouble recognizing and getting rid of abnormal cells, bacteria and viruses. However, once cancer develops, your immune system may not recognize cancer cells as abnormal, or may not be able to fight them. In fact, cancer cells have been shown to block the immune system’s natural response, which can allow cancer to grow and spread throughout the body.

The immune system can recognize viruses, bacteria and even cancer cells by responding to signals called “antigens”, which are not normally expressed by healthy or normal cells. Once discovered, the immune system processes these foreign “antigens” and mounts a response.